In the early part of the 20th century, long-distance telephone companies, primarily ATandT/Bell Telephone, made significant investments to establish an infrastructure of trunk lines running between the major cities. During the past 30 years, telephone companies have sought to upgrade this infrastructure with systems capable of high-speed digital connections.
To accomplish this conversion, trunk circuits and switching systems have been redesigned from analog to digital equipment. In older analog systems, each wire pair in the copper cable comprised a dedicated circuit supporting only one voice or data connection. Because of the high cost of copper cable, special equipment was developed to carry more than one speech conversation on a pair of wires. This technique, known as multiplexing, combines the data from several telecommunications devices onto one communications circuit. At the other end of the circuit, another multiplexer splits the data and routes it appropriately. The two common types of multiplexing are frequency multiplexing and time division multiplexing. Frequency division multiplexing, which involves dividing a trunk line""s available bandwidth into discrete frequency bands, was used for transmitting multiple analog circuits via one pair of twisted copper wires. Time division multiplexing (TDM), which allocates discrete, reiterated time slots for each circuit, was developed to accommodate multiple digital transmission services sent over a single circuit.
In conjunction with TDM, the T1 digital carrier system was developed in the 1960""s as a short distance transmission system for carrying digital signals over a single twisted pair of copper wires without interference. The bandwidth of a T1 line is 1.54 Mbps, yielding a capacity for 24 64 kbps digital channels and 8 kbps for keeping the ends of the trunk synchronized by imposing a framing process. To make use of the T1 system, voice signals are required to be converted into digital format, generally using a pulse code modulation (PCM) encoding scheme.
Conversion of voice and other analog sources to digital format is carried out by a channel bank, which samples each of the 24 analog circuits at a rate of 8000 times per second to produce a snapshot of the analog signal at precisely synchronized instants. The amplitude of the snapshot is rounded off the nearest of several specific, predetermined levels, in a quantization process. The quantized snapshot level is converted into an 8 bit binary representation of the analog signal. Thus, every channel is represented by an 8 bit PCM byte for analog signals, or one data byte for digital signals.
The term xe2x80x98channel bankxe2x80x99 is used because it may contain sufficient processing power to encode to digital format a bank of up to 24 individual channels per T1 port, and to decode these channels as well. Thus one channel bank encoding up to 24 channels may generate the composite digital signal to feed one T1 circuit, and a channel bank is required at either end of the T1 circuit.
Modern T1 circuits are formed by two twisted-pair cables (four wires total), enabling nodes at either end of a T1 line to transmit and receive in both directions simultaneously in full duplex mode. A T1 multiplexer divides a T1 line into 24 separate 64 kbps channels, each channel comprising a digital signal level 0 (DS-0). The multiplexed T1 signal format is termed digital signal level 1 (DS-1). The T1 digital carrier system can carry both data and nondata traffic, such as voice and video, because all these types of transmitted information can be digitally encoded. Therefore, the T1 line can carry xe2x80x9cintegratedxe2x80x9d traffic so that a customer does not need to have separate lines (or trunks) for voice, video, and data.
A multiplexer placed at each end of a T1 line acts like a funnel allowing multiple sources and formats to be mixed at the transmitting end and to be extracted and appropriately routed at the receiving end. A T1 multiplexer typically consists of a T1 interface, a strobe unit, a power source, and control logic. Multiplexer devices also usually contain open slots to accommodate various types of channel cards, such as circuit cards or feature cards. The two most common types of channel cards are designed to support voice or data applications. A voice card provides a connection to an analog circuit, and carries out the digital to analog and analog to digital conversions. A data card provides a connection to a digital circuit, and may reformat or reframe the signal. The T1 multiplexer combines the digital signals from the voice and data channel cards and combines them into a single 1.544 Mbps circuit of 24 DS-0s.
For users who need less than 1.544 Mbps bandwidth, telecommunication companies offer fractional T1 service, allowing users to pay for the portion of the T1 bandwidth they use. This approach makes leased services more affordable for small businesses. For users who require more than the T1 bandwidth, telecommunications companies offer T3 trunks with a capacity of 28 multiplexed T1 lines, equivalent to 672 DS-0s, with a bandwidth of 44.7 Mbps. The T3 line is referred to as a digital signal level 3 (DS-3) channel.
Although the multiplexing and transmission of telecommunications traffic appears straightforward in conceptual terms, the actual task of setting up and managing a telecommunications system is extremely complex. A wide variety of input signals must be accepted, such as analog and digital voice, data, video, fax, modem, LAN/WAN, internet and intranet, and the like. These inputs may have differing protocols, framing, and timing, and must be reliably synchronized, transmitted and decoded. Circuits must be set up and maintained without interruption or fault, and signals must be routed to and from a large number of telecommunications devices. Bandwidth requirements may change on a regular basis, according to workday schedules, or may change abruptly due to unexpected demands. At any node on a transmission system, some channels may be required to be unloaded and replaced with other signals, whereas other channels may be passed through the node without alteration. These factors all contribute to an extremely complex signal processing environment.
In one aspect, the present invention generally comprises a modular, reconfigurable, intelligent signal multiplexer for telecommunications purposes. The multiplexer is comprised of a rack or shelf adapted to support a plurality of printed circuit cards. The cards may include feature cards, such as line cards, and at least one central controller card. All of the cards includes backplane connectors that are adapted to connect to customer premises equipment and to telecommunications lines and networks. The cards further include midplane connectors that are adapted to interconnect all of the circuit cards for data exchange under program control.
Each feature card also contains an embedded microprocessor with associated embedded operating system, as well as RAM memory and flash RAM. Consequently, all cards are software-independent, thereby reducing or eliminating the need for systemwide software upgrades. This design also facilitates system upgrades and new feature card installation without requiring new common equipment. Software control of the feature cards resides in the cards themselves, instead of residing within the central controller card.
The signal multiplexer processes digital inputs from a wide range of user equipment for transmission over digital facilities, including T1 and T3 lines. The trunk bandwidth is managed with programmable bandwidth allocation, which enables the service provider to allocate bandwidth to specific customers on an as-needed basis, and to alter the bandwidth allocation virtually instantaneously. The system employs a Simple Network Management Protocol (SNMP) to perform network configuration as well as to obtain performance reports, statistics collection and alarm monitoring. SNMP is accessed through a SNMP network manager or web browser that provides an intuitive graphical interface for network routing and inventory-management support. In this regard, the central controller card provides all common, management plane control functions, and is provided with a SNMP master agent and an on-board Web server that works with SNMP via a non-graphic terminal interface. Each feature or line card is provided with a SNMP agent on-board. The central controller card also has an on-board modem, and users can control the multiplexer functions from one central workstation, using a LAN or PPP connection.
SNMP is a standardized software package for managing network equipment, and is designed to facilitate the exchange of information between network devices. Network components from a plurality of manufacturers can be controlled using SNMP, as long as all the components support SNMP. The system requires a single SNMP manager or master agent at a central management site and a SNMP subagent at each component site, and a suitable data path therebetween.
The primary function of the signal multiplexer, which is assembly and transmission of telecommunications signals, is achieved by a mapping process in which all of the DS-0 time slots of the T1/T3 lines are assigned to the line cards. A map change alters the circuit-to-time slot assignments, and, by changing to a new working map, the system is able to change time slot assignments without causing data errors on unchanged DS-0s. A large number of maps may be stored by the system. Maps are set to start running in response to user-specified times, a predetermined event, an alarm, or a manual keyboard command. Maps may be set, changed, and verified using standard and enterprise MIBs, through the graphical user interface and verified by SNMP.
Time-triggered maps reconfigure the multiplexer automatically at a specified time. For example, voice circuits can be decreased, and high speed data capacity can be increased for evening and weekend operations, when few employees are using voice circuits. This feature allows data backups and file transfers to be processed more quickly during off-peak hours. Event-triggered maps are switched on by an event, such as a disaster situation or a demand requirement; e.g., a video transmission or the like. Alarm-triggered maps are switched on by predetermined alarm conditions, such as Bit Error Rate Alarm, or Red or Yellow Alarms. The system supports common Bell System alarms, including Local alarm, Remote alarm, and Carrier Group Alarm (CGA).
The use of the graphical user interface network manager (hereinafter, Advanced Intelligent Multiplexer Network, or AIMNET) in conjunction with the system mapping approach enables the intelligent multiplexer to provide unique features not found in the prior art. Functions such as drop-and-insert multiplexing, digital cross-connect, and virtually instantaneous reconfigurability may be applied to the transmission system through AIMNET management software.
In another aspect of the invention, the user interface software includes a graphical user interface that presents iconic representations of network connections, and enables the user to define nodes and draw graphic links therebetween on a video display. The network layout software then facilitates the design of the network nodes and connections using a graphic interactive presentation to the user. The user can specify the number of line cards in each intelligent multiplexer at each node and the node connections, and can move and re-arrange these objects on-screen. After the network topology is laid out on-screen, the user may add spans, which are actual circuits, to the links, which are logical pathways. Spans may include T1 and T3 circuits.
The program requires that sufficient line cards are present at each node to support the spans added on-screen. In this regard, the program also provides a pop-up context menu that permits the user to modify the equipment at each node during the process of laying out the spans of the network. The program also provides interactive screen displays that enable selection of span configurations, source node and destination node, source card/port and destination card/port, and type (T1, T3, etc.). The user can first select the type of span they wish to add, and the software searches both nodes for compatible line interface units, and then displays the first compatible card it finds as well as the card information, including slot number, port number, and available bandwidth.
Users can navigate through the ports on the cards, or through the cards themselves, using an up/down spinner control. The availability of the ports for interconnection is indicated by the color of arrows displayed in a dialog box: yellow to indicate that connection is possible at the bandwidth shown, red to show that a connection is not possible because the respective port is already connected in another span, and green to indicate that two ports are already connected on the selected span. The system includes follow-on interactive screen displays to enable port connections, and trunk connections. Once the design is completed on-screen, it must be translated into an appropriate map and sent to all the nodes, using a combination of User Datagram Protocol (UDP) and Transmission Control Protocol (TCP). These maps can include time of day and day of week constraints.
At the real nodes which correspond to the graphical node representations used in the on-screen design process, each node is polled to verify that all the cards assignedto each node are actually in place, and that the card slots are properly configured. Node configuration data is displayed on-screen, and update requirements may be entered. Likewise, routing tables for each node may be received, examined, and updated. The network design may then be implemented. As noted above, maps formed in the process described above may be stored, and invoked or swapped automatically, or in response to an alarm condition, or by manual command.
Each feature card may be addressed individually, so that line cards may be remapped individually and/or serially, or may be remapped simultaneously. If only one or more line card is altered, the remaining cards may remain in operation without interruption. This permits xe2x80x9chot-swappingxe2x80x9d or addition and replacement of line circuit cards while the multiplexer remains in full running status.
The use of the graphical user interface network manager AIMNET in conjunction with the system mapping approach also enables fault tolerant design features not found in the prior art. The network manager may be used to assign a priority value to any channel connected thereto. If one or more of the internode spans becomes non-functional or unavailable, this occurrence is treated as a triggering event, and AIMNET responds by rerouting the channels on the functioning spans so that communications traffic having higher priority is routed first, while the lowest priority traffic may be sacrificed. AIMNET can also configure a system to operate in a redundant mode, in which each node operates with fully duplicated critical components: two power supplies and fan assemblies, and two central controller circuit cards. If a critical component fails, the system will switch to the backup component with a minimum of disruption. Likewise, a node may be configured with redundant T-3 line interface cards, one being active and the other being standby. In the event of a failure of the active LIU, the central controller of the node will detect the failure, activate the standby LIU and remap all circuits to the newly activated card.
The system may also be set up as an active ring, in which a plurality of D/I MUX nodes has incoming and outgoing T-1 spans connected to other nodes in a closed loop that includes one fully configured AIM node. Each node is assigned channels from the 24 available and operates in a drop-and-insert mode. In the event of a T-1 span failure, the fully configured node will loop its transmit and receive circuit to reconstitute the loop, and operation will resume with little disruption.